Revamping nanotubes

Recycling carbon nanotube waste into nanocomposite plastic materials for industrial purposes may not be as easy as recycling plastic.

Carbon nanotubes (CNTs) are set to become an important material for the future. That’s because they are light, robust, and highly conductive, both electrically and thermally whilst still being chemically stable. They are used in broad variety of applications ranging from bicycle components to hydrogen storage. The trouble is that the nanotube manufacturing process is not as sustainable and cost-effective as it could be.

The RECYTUBE project, funded by the European Union, aims to reuse CNT scraps created during production to turn them into new plastic nanocomposites. “Conductive polymers need very specific and expensive fillers, so the project is studying how to recycle CNT production waste to make these fillers more cheaply and easily than is currently done,” explained Pascual Martinez, technical and research engineer at Faperin S.L., Ibi, Spain, one of the project’s technical leads. “We have already produced some injected plastic pieces of reused conductive polymer to demonstrate this.”

The critical test for the project will be whether such a solution is taken up by industry. Some believe the main driver would be to save costs. “There is tremendous growing interest in using reprocessed plastics, both in form of regrinds and re-granulates; mainly due to cost reasons in the commodity sector,” Klaus Mauthner, head of research and development at C-Polymers, Tresdorf, Austria, tells. He adds: “with nano-composites it could work in the same way.”

However recycling of CNT may not be as easy as with plastics. Mauthner explain that he is “concerned if there is already enough material circulating and if the labelling is obvious enough to make collection and separation feasible.” He expresses his scepticism: “waste from moulding or extrusion, it’s of course no problem, but post-lifetime recycling aiming at nanocomposite-remake, I regard as doubtful at the moment.”

The project’s output could find use in industry as construction material. “The idea of recycling materials containing nanotubes is very good,” says Andrei Khlobystov, Professor of nanomaterials at the University of Nottingham, UK, “Nanotubes are already well-dispersed… in the scrap material, so they can be integrated in new materials more readily, using less energy and chemicals.”

Potential applications will however be limited by the quality of the final product. “Considering CNTs are very strong mechanically and thermally, recycling should not affect their key functional properties, which are important for this project,” Khlobystov says, “however, some deterioration of the nanotube surfaces may occur.” And this is not the only challenge ahead. Mauthner explains: “Large volume recovery of CNT-composite waste from various sources will require R&D activities to develop the necessary knowledge and experience in order to create materials of high quality.”